1. Field of the Invention
The present invention relates to an image forming method and apparatus for generating an image recording liquid having a predetermined density and/or a predetermined color by changing a mixing proportion of plural coating liquids based on an image signal, and leading the image recording liquid as a continuous flow to an image receiving medium to form an image.
2. Description of Related Art
U.S. Pat. No. 4,109,282 discloses a printing device, in which a valve called a flap valve is disposed in a flow path for leading two types of liquid, that is, clear ink and black ink into an image forming substrate. The flow path for each ink is opened/closed by displacing this valve so that the two types of liquid are mixed by a kept/fixed total amount in a desired density to be transferred onto the substrate. This enables printout of an image having gray scale information which is the same as that of the image information displayed on a TV screen.
This patent discloses that a voltage is applied between the flap valve and an electrode provided on an surface opposite to the flap valve and the valve itself is mechanically deformed by an electrostatic attracting force to displace the valve. Furthermore, the ink is absorbed in paper by a capillary action which acts on the ink between a tip end of the flap valve and fibers of a print paper.
Unexamined Japanese Patent Publication (KOKAI) No. 291663/1988 discloses a coating method, in which two types of thick (dark) and thin (light) liquid are mixed in a coating head to be continuously extruded from a slot-opening opposed to a running web. Thus, the mixed liquid is consecutively coated on the web. In this coating method, the mixed liquid is coated over the entire coating width with a uniform coating membrane pressure without forming residue deposit, and the coating liquid having a density graduation in time course is, continuously applied with respect to a traveling direction of the web. In addition, this method enables coating with a uniform thickness with respect to the width direction.
According to the method disclosed in the U.S. Pat. No. 4,109,282, the ink extruded from the nozzle is directly applied on the paper. Therefore, when the paper has a large thickness or irregularity on a surface, it is difficult to reproduce an image on the paper with fidelity with respect to the electric signal. Accordingly, this method has not been practically used yet. Further, since the ink to be used is restricted to two types, a color image cannot be recorded.
Furthermore, since the ink is drawn out by the capillary action between the ink and the fibers of the paper in this mode, the ink tends to be affected by paper quality and a change in the paper quality involves a change in an image quality. Moreover, the image cannot be truly reproduced due to the partial irregularity of the fiber structure even if the paper with the same quality is used.
According to the method disclosed in the Unexamined Japanese Patent Publication (KOKAI) No. 291663/1988, although the image having the density graduation along the traveling direction of the web which is a coating target can be formed, the image cannot have a density graduation along a width direction of the web (a direction perpendicular to the traveling direction). Consequently, application of the coating liquid whose color or density changes for each pixel in accordance with an image signal is impossible.
Therefore, the present applicant has proposed an image forming method (continuous coating method) of changing a mixing proportion of a plurality of coating liquids based on an image signal to extrude a continuous flow from a plurality of coating liquid extruding ports, and continuously coating an image receiving medium with the continuous flow of the image recording liquid (Japanese Patent Application No. 374662/1998;
U.S. patent application Ser. No. 09/472,977). Moreover, when the image receiving medium is continuously coated with the image recording liquid, distortion of a stream line of image recording liquid occurs in a bead formed on an upstream side of a coating portion, and the image quality is deteriorated. In order to prevent this stream line distortion, the present applicant has also proposed a method of applying a clear undercoating liquid between the image recording liquid and the image receiving medium (Japanese Patent Application No. 374663/1998; U.S. patent application Ser. No. 09/472,974).
However, in these continuous coating methods, on both edges of an image forming width the image recording liquid is raised and thickened, or spread over and thinned in a width direction. Therefore, an image density rises or decreases particularly in the vicinity of both edges of the image forming width and an image quality is deteriorated by the, distorted stream line of the image recording liquid.
Moreover, in these continuous coating methods, in a front edge (edge of the image receiving medium in a moving direction) or a rear edge (edge in a direction reverse to the moving direction) of an image forming area, the image recording liquid becomes thick as compared with a central portion of the image forming area, or is spread on the front edge or the rear edge and thinned. Moreover, a position of the image recording liquid may change. Therefore, the thickness of the image recording liquid is distorted particularly in the vicinity of the front edge or the rear edge of the image forming area, resulting in that no desired image quality or density can be obtained.
The present invention has been accomplished under the aforementioned circumstances, and a first object thereof is to provide an image forming method by which a thickness or a stream line of an image recording liquid can be prevented from being distorted in the vicinity of both edges of an image forming width in a continuous coating method, and a stable and good-quality image can be formed. A second object is to provide an image forming apparatus for direct use in implementing the method.
Moreover, a third object of the present invention is to provide an image forming method by which a thickness or a position of an image recording liquid can be prevented from changing in the vicinity of a front edge and/or a rear edge of an image forming area in a continuous coating method, and a stable and good-quality image can be formed. A fourth object is to provide an image forming apparatus for direct use in implementing the method.
According to the present invention the first object is attained by an image forming method for forming an image on an image receiving medium with an image recording liquid, comprising steps of:
a) combining a plurality of recording liquids to form said image recording liquid, a mixing ratio of the plurality of recording liquids being varied based on an image signal;
b) extruding said image recording liquid from an image recording liquid extruding port to the image receiving medium as a continuous flow while the image receiving medium is moved relatively to the extruding port, so that said image recording liquid is continuously transferred to the image receiving medium to form the image; and
c) extruding a dummy liquid for forming no image from a dummy liquid extruding port to the image receiving medium;
wherein to said image receiving medium, the image recording liquid is transferred in an image forming width, and a dummy liquid for forming no image is transferred to the outside of said image forming width.
In the present invention, the dummy liquid for forming substantially no image is applied outside the image forming width. This prevents both edges of the image recording liquid from being raised and thickened on the image receiving medium or being spread out in a width direction, prevents an image density from rising or lowering in the edge of the image and can prevent a stream line of the image recording liquid from being distorted. Therefore, an image quality can be enhanced.
The image recording liquid within the image forming width and the dummy liquid outside the image forming width may deviate in time from each other during transferring. However it is preferably to combine the both liquids in a direction perpendicular or substantially orthogonal to the relative moving direction of the image receiving medium and simultaneously transfer the liquids as a zonal continuous flow. It is desirable to set at least one of a surface tension and a viscosity of the image recording liquid and the dummy liquid in the vicinity of a contact portion of both liquids to be substantially the same, and to smoothly continue a boundary of the liquids. By setting both liquids substantially the same temperature at least when both liquids come into contact with each other, the boundary of the liquids can further be smoothed, and the distortion can be reduced.
A plurality of dummy liquid extruding ports may be disposed on at least one outer side of the image forming width, and an extruding width of the dummy liquid can be changed and appropriately set. The extruding width of the dummy liquid is set to a width for one or more pixels, and may be increased in accordance with an ink coating thickness. Usually, the width is preferably several tens of micrometers. In this case, by changing the dummy liquid extrusion amount from each dummy liquid extruding port, the thickness of the dummy liquid on the image receiving medium can be uneven in the width direction For example, by setting a volume flow rate per unit width of the dummy liquid not to exceed the volume flow rate per unit width of the image recording liquid, or gradually reducing the thickness of the dummy liquid on the image receiving medium toward the outside of the width direction, the dummy liquid can further be stabilized on the image receiving medium. This can further securely prevent the image quality from being distorted.
When the image recording liquid extruding port can also be used as (diverted to) the dummy liquid extruding port, even a change of the image forming width can easily be handled without replacing a recording head. The dummy liquid is preferably a clear liquid (image non-forming liquid) containing substantially no image forming substance. Moreover, when at least one of the plurality of recording liquids constituting the image recording liquid is substantially used as the image non-forming liquid for forming substantially no image after image formation, the density can be adjusted by changing a mixing proportion of the image non-forming liquid and another recording liquid. The dummy liquid can be the same as at least some image non-forming liquids among the recording liquids which form the image recording liquid. In this case, types of liquids for use can be reduced. Moreover, by keeping the volume flow rate of the image recording liquid extruded from the image recording liquid extruding port to be substantially constant, transferring of the image recording liquid to the image receiving medium from the recording head can be stabilized, which is suitable for image quality enhancement.
The second object of the present invention is attained by an image forming apparatus for forming an image on an image receiving medium with an image recording liquid, comprising:
a recording head having an array of plural image recording liquid extruding ports and a dummy liquid extruding port, the array of the plural image recording liquid extruding ports being aligned in a direction perpendicular to a relative moving direction of the image receiving medium within an image forming width, the respective image recording liquid extruding ports extruding plural recording liquids and combining the plural recording liquids to form said image recording liquid, the image recording liquid being transferred to the image receiving medium as a continuous flow while the image receiving medium is moved relatively to the aligned plural image recording liquid extruding ports, the dummy liquid extruding port being disposed adjacent to the outside of the image forming width and extruding a dummy liquid;
image recording liquid extrusion amount control means for controlling supply amounts of the recording liquids fed to said respective image recording liquid extruding ports;
dummy liquid extrusion amount control means for controlling an extrusion amount of the dummy liquid extruded from the dummy liquid extruding port; and
a controller for controlling said image recording liquid extrusion amount control means and said dummy liquid extrusion amount control means;
wherein said controller determines a mixing proportion of the plural recording liquids in the image recording liquid based on an image signal, and determines a supply amount and a supply timing-of the respective recording liquids and the determined the supply amount and supply timing is fed to said image recording liquid extrusion amount control means;
wherein said controller determines a supply amount and supply timing of the dummy liquid extruded from the dummy liquid extruding port and the determined supply amount and supply timing of the dummy liquid is fed to said dummy liquid extrusion amount control means.
The controller determines the mixing proportion of the coating liquids to be led to the respective image recording liquid extruding ports based on the image signal, and controls color and/or density of a mixture liquid. A plurality of recording liquids to form the mixture liquid (image recording liquid) are extruded as a continuous flow from the image recording liquid extruding port within the image forming width, and transferred to the image receiving medium together with the dummy liquid extruded from the dummy liquid extruding port outside the image forming width. As a result, the image is formed on the image receiving medium. Since the image recording liquid is transferred as the continuous flow with both edges held by the dummy liquid, the image recording liquid fails to be spread over in the width direction, and a high-quality image can be formed.
When a plurality of dummy liquid extruding ports are disposed on at least one outer side of the image forming width, adjustment of dummy liquid extrusion amount or extrusion width of the dummy liquid can easily be performed. By continuously arranging the image recording liquid extruding ports and dummy liquid extruding port in the width direction of the recording head, the image recording liquid and dummy liquid can simultaneously be transferred to the image receiving medium. When the dummy liquid can also be used as (can mutually be diverted to) the image recording liquid extruding port, the change of the image forming width can easily be handled.
In the recording head, a slot-shaped opening may be provided for connecting the image recording liquid extruding port to the dummy liquid extruding port in the width direction and combining the image recording liquid and dummy liquid in the width direction to extrude the integrated liquids in a strip shape. In this case, the image recording liquid can further steadily be transferred to the image receiving medium together with the dummy liquid. The recording head may be provided with a slot-shaped opening for extruding and applying an undercoating liquid. By applying the undercoating liquid from the slot-shaped opening, and transferring the image recording liquid and dummy liquid onto the undercoating liquid in a superposed manner, the stream line of the image recording liquid is prevented from being distorted and the image quality can further be enhanced.
The image receiving medium may be an intermediate image receiving medium to which the recording liquid extruded from the image recording liquid extruding port is transferred. The image recording liquid temporarily held on the intermediate image receiving medium is transferred to a final image receiving medium such as a recording sheet. In this case, the undercoating liquid can be used as a layer in contact with the surface of the intermediate image receiving medium to cover the surface of a final image when transferred to the final image receiving medium.
The extrusion amount control means can be formed by a control valve disposed on a passage extending from a feed path for supplying the recording liquid to the recording liquid extruding port. For example, the means may be formed by a diaphragm valve using a piezoelectric element. This extrusion amount control valve is disposed for each of pixels arranged in the width direction of the recording head, and the flow rate is controlled by either one of a valve opening degree, opening time, and opening frequency, or a combination of these. Moreover, the extrusion amount control means may be formed by a pump with a variable extrusion amount. This pump may be constituted, for example, of the piezoelectric element disposed for each of the pixels arranged in the width direction of the recording head, and a check valve. In this case, the flow rate is controlled by either one of an operation speed, operation time, and operation frequency of the pump, or a combination of these.
The coating liquids, i.e., image recording liquid and dummy liquid, can be transferred from the recording head to the image receiving medium by various kinds of modes. For example, it is possible to adopt a slot coating method by which the coating liquid extruding ports is formed on the top surface, the bottom surface or the side surface of the recording head and the image receiving medium is moved along the surface having the extruding ports with maintaining a predetermined gap from the surface. The coating liquids are extruded and guided to the gap between the surface of the recording head and the image receiving medium to form an image.
Additionally, it is possible to use a slide coating method by which a sloped surface which inclines toward the image receiving medium is formed on the top surface of the recording head and the coating liquids extruded on the sloped surface flow down to form a bead at the lower end of the sloped surface where the coating liquids meet the image receiving medium which is moving thereby, so that an image is formed or recorded on the image receiving medium. Moreover, a curtain coating method may be adopted, in which the coating liquids supplied from the recording head flow down along a guide plate onto the image receiving medium.
Although the image receiving medium itself may be a final image receiving medium such as print paper, it may be an intermediate image receiving medium. In this case, the intermediate image receiving medium is provided between the recording head and the final image receiving medium and transfer the coating liquids fed from the recording head to the final image receiving medium, and it may have a drum-like shape or an endless belt-like shape.
The third object of the present invention is attained by an image forming method for forming an image on an image receiving medium with an image recording liquid, comprising steps of:
a) combining a plurality of recording liquids to form said image recording liquid, a mixing ratio of the plurality of recording liquids being varied based on an image signal;
b) extruding said image recording liquid from an image recording liquid extruding port to the image receiving medium as a continuous flow while the image receiving medium is moved relatively to the extruding port, so that said image recording liquid is continuously transferred to the image receiving medium to form the image; and
c) extruding a dummy liquid for forming no image from a dummy liquid extruding port to the image receiving medium;
wherein said dummy liquid is transferred to said image receiving medium so that the transferred dummy liquid adjoins at least one of a front end and a rear end of an image forming area to which the image recording liquid is transferred.
In this mode of the present invention, the dummy liquid for forming substantially no image is transferred to the fore end and/or the rear end of the image forming area. This prevents the front edge and/or the rear edge of the image recording liquid from spreading onto the image receiving medium, and can prevent the image from being distorted on the front/rear edge of the image. Therefore, the image quality can be enhanced.
In order to transfer the dummy liquid to the front-end side of the image forming area, the dummy liquid may be transferred to the image receiving medium after the extruding from the dummy liquid extruding port is stabilized.
Judgment on whether or not the extruding from the dummy liquid extruding port is stabilized can be performed by an output of a bubble detection sensor disposed in the vicinity of a dummy liquid extruding port. Specifically, when the dummy liquid contains a bubble, the extruding becomes unstable.
The bubble detection sensor can radiate laser light to the surface (hereinafter referred to as an extrusion surface) of the dummy liquid extruded from the dummy liquid extruding port, and monitor the laser light reflected by the dummy liquid surface (extrusion surface). This constitution can be formed by a laser light source, a scanning optical system for scanning the laser light to the dummy liquid extrusion surface, and a light receiving element for receiving the reflected light.
In order to prevent the dummy liquid from being transferred to the image receiving medium before the extruding of the dummy liquid is stabilized, the recording head may be disposed apart from the image receiving medium. Additionally or alternatively, a liquid recovery section is disposed midway in a transfer path of the dummy liquid to the image receiving medium from the dummy liquid extruding port, and the unstably extruded and unnecessary dummy liquid is removed and recovered before reaching the image receiving medium.
In order to transfer the dummy liquid to the rear end of the image forming area, the transferring to the image receiving medium may be ended before the extruding of the dummy liquid is stopped, in other words, before the extruding becomes unstable. By regulating the transferring of the dummy liquid to the image receiving medium while the extruding of the dummy liquid is stable, the unstably extruded dummy liquid is prevented from being applied to the image receiving medium, which is suitable for the image quality enhancement. In order to prevent the unstable dummy liquid from being transferred to the image receiving medium, the recording head is detached from the image receiving medium while the dummy liquid is stable. Additionally or alternatively, the liquid recovery section may be disposed midway in the transfer path of the dummy liquid to the image receiving medium from the dummy liquid extruding port. While the extruding of the dummy liquid to be transferred to the rear end of the image forming portion is stable, the liquid recovery section starts operating to prevent the dummy liquid from being transferred to the image receiving medium.
In addition to the front end or the rear end of the image forming area, the dummy liquid may be transferred to at least one outer side of the width direction. This not only prevents the image from being distorted on the front-end side or the rear end of the image forming area, but also prevents the image from being distorted in the edge of the width direction of the image forming area.
The image recording liquid transferred within the image forming area and the dummy liquid transferred to the front end or the rear end of the image forming area or to the outside of the width direction may deviate from each other in time and be applied. Preferably, the liquids are combined as a strip-shaped continuous flow in a direction substantially perpendicular to the relative moving direction of the image receiving medium and successively transferred continuously in time. For the image recording liquid and dummy liquid, by setting at least one of surface tension and viscosity to be substantially the same in the vicinity of the contact portion of both liquids, the boundary of both liquids may preferably smoothly be continued. By setting the same temperature at least when both liquids come in contact with each other, the boundary of both liquids can further be smoothed, and the distortion can be reduced.
By arranging a multiplicity of dummy liquid extruding ports in the direction completely or substantially crossing at right angles to the relative moving direction of the image receiving medium, the transfer width of the dummy liquid may appropriately be set in accordance with the image forming width. In this case, by changing the dummy liquid extrusion amount from each dummy liquid extruding port, the coating thickness of the dummy liquid can be uneven in a length direction of the image forming area, that is, in the relative moving direction of the image receiving medium. For example, by setting the volume flow rate per unit transfer length of the dummy liquid not to exceed the volume flow rate per unit transfer length of the image recording liquid, or gradually reducing the transfer thickness of the dummy liquid toward the front or the rear of the image forming area, a dummy liquid transfer portion can further be stabilized, and the image quality on the front or rear edge of the image forming area can further be improved.
When the image recording liquid extruding port can also be used as (diverted to) the dummy liquid extruding port, even the change of the image forming width can easily be handled without replacing the recording head. The dummy liquid is preferably a clear liquid (image non-forming liquid) containing substantially no image forming substance. Moreover, when at least one of the plurality of recording liquids constituting the image recording liquid is substantially used as the image non-forming liquid for forming substantially no image after image formation, the density can be adjusted by changing the mixing proportion of the image non-forming liquid and another recording liquid. The dummy liquid can also be the same as at least some image non-forming liquids which form the image recording liquid. In this cases the types of liquids for use can be reduced. Moreover, by keeping the volume flow rate of the image recording liquid extruded from the image recording liquid extruding port to be substantially constant, the transferring of the image recording liquid to the image receiving medium from the recording head can be stabilized, which is suitable for the image quality enhancement
The fourth object of the present invention is attained by an image forming apparatus for forming an image with an image recording liquid comprising:
a recording head having an array of plural image recording liquid extruding ports and a dummy liquid extruding port, the array of the plural image recording liquid extruding ports being aligned in a direction perpendicular to a relative movement direction of the image receiving medium within an image forming width, the respective image recording liquid extruding ports extruding plural recording liquids and combining the plural recording liquids to form said image recording liquid, the image recording liquid being transferred to the image receiving medium as a continuous flow while the image receiving medium is moved relatively to the aligned plural image recording liquid extruding ports, the dummy liquid extruding port being disposed to cover the image forming width and extruding a dummy liquid to;
image recording liquid extrusion amount control means for controlling supply amounts of the recording liquids fed to said respective image recording liquid extruding port;
dummy liquid extrusion amount control means for controlling an extrusion amount of the dummy liquid extruded from the dummy liquid extruding port; and
a controller for controlling said image recording liquid extrusion amount control means and said dummy liquid extrusion amount control means;
wherein said controller determines a mixing proportion of the plural recording liquids in the image recording liquid based on an image signal, and determines a supply amount and a supply timing of the respective recording liquids and the determined supply amount and supply timing is fed to said image recording liquid extrusion amount control means;
wherein said controller determines a supply amount and supply timing of the dummy liquid extruded from the dummy liquid extruding port and the determined supply amount and supply timing of the dummy liquid is fed to said dummy liquid extrusion amount control means, so that the dummy liquid is transferred to at least one of a front end and a rear and of an image forming area to which the image recording is transferred.
By individually arranging the image recording liquid extruding ports and the dummy liquid extruding port continuously in the width direction of the recording head, the image recording liquid and dummy liquid can successively be transferred to the image receiving medium in a time deviating manner. When the dummy liquid and image recording liquid extruding ports can be used in a combined manner (can be diverted to each other), the dummy liquid can be transferred not only to the front end or the rear end of the image forming area but also to the outside of the width direction, and even the change of the image forming width can easily be handled.
When the image recording liquid extruding port and dummy liquid extruding port are used in the combined manner, and when the dummy liquid can also be transferred to the outside of the width direction of the image forming area, the recording head may be provided with a slot-shaped opening for connecting the image recording liquid extruding port to the dummy liquid extruding port in the width direction and for combining the image recording liquid and dummy liquid in the width direction to extrude the liquids in the strip shape. In this case, the image recording liquid can further steadily be transferred to the image receiving medium together with the dummy liquid. The recording head may be provided with a slot-shaped opening for extruding and applying an undercoating liquid. By transferring the undercoating liquid from the slot-shaped opening, and transferring the image recording liquid and dummy liquid onto the undercoating liquid in the superposed manner, the thickness or position of the image recording liquid is prevented from being distorted and the image quality can further be enhanced.
The image receiving medium may be sheet shaped such as paper or film shaped, so that the image recording liquid and the dummy liquid may be transferred to the image receiving medium directly by the recording head. Alternatively, the image recording liquid may be transferred to the final image receiving medium such as paper via the intermediate image receiving medium such as a transfer drum. In this case, by performing a surface treatment to stabilize a surface state of the intermediate image receiving medium, an influence of fluctuation of the surface state of the final image receiving medium is prevented from being easily exerted, and a high-quality image can further be formed. Moreover, the liquid recovery section can be disposed in the intermediate image receiving medium.
When the image is transferred to the final image receiving medium via the intermediate image receiving medium, the liquid recovery section may be disposed in the intermediate image receiving medium. The liquid recovery section may be formed by a blade which can be attached to or detached from the surface of the intermediate image receiving medium. Specifically, by pressing the blade onto the surface of the intermediate image receiving medium, the liquid transferred to the surface of the intermediate image receiving medium is removed and recovered, and is prevented from being transferred to the final image receiving medium.
The controller transfers the dummy liquid prior to the image forming liquid, and transfers the image recording liquid continuously after the dummy liquid. In order to transfer the image recording liquid, the controller determines the mixing proportion of a plurality of recording liquids to be led to is the respective image recording liquid extruding ports based on the image signal, and controls the color or density of the mixture liquid. A plurality of recording liquids forming the mixture liquid (image recording liquid) are extruded as the continuous flow from the image recording liquid extruding port within the image forming width.
When the image recording liquid is extruded, the dummy liquid may simultaneously be extruded from the dummy liquid extruding port outside the image forming width. In this case, the dummy liquid is transferred to the image receiving medium together with the image recording liquid. As a result, the image is formed on the image receiving medium. Since the image recording liquid is transferred with the front edge and/or the rear edge held by the dummy liquid, the thickness or position of the front edge and/or the rear edge of the image recording liquid is stabilized, and the high-quality image can be formed. When the dummy liquid is also transferred to the outside of the image forming width, the image quality of the edge of the width direction of the image fails to be distorted, and the image quality is further enhanced.
In the present invention, the image formed on the image receiving medium includes graphical intelligence patterns such as alphanumeric characters, graphical display, line art, and other image information.